What injury does Justyce have after the event with Officer Castillo? What caused the injury?

In Part I, Justyce responds to a 3 a.m. call that his ex-girlfriend Melo needs help. He walks over from his friend Manny’s house and finds Melo in a parking lot. Despite her intoxication and hostility, Justyce still finds her half-black, half-Norwegian beauty attractive. As he tries to lift her into the car, she vomits on his prep school hoodie. Justyce considers just calling her parents, but she is unconscious and vulnerable. When Justyce lifts her into her car's backseat, a police officer handcuffs him and slams him to the ground. Justyce tries to explain the misunderstanding; but, the officer hits him across the face and swears at him,citing his hoodie as proof of bad intentions toward this white girl (8). Justyce reads his nameplate: “Castillo” (8).

The handcuffs cause his wrists to swell and bruise.